This invention relates to means for causing a member, such as an arm, to oscillate back and forth (vibrate) and, in particular, to means for causing the member to vibrate with very little power consumption.
In certain applications, such as a bar code reader, it is necessary to scan, or sweep, a light beam across a target, such as a bar code, and to receive the light reflected from the bar code to subsequently decode the information encoded in the bar code. FIG I illustrates the format a bar code may have (parallel bars of different widths and spacing) and a laser light beam sweeping across the bar code (i.e. the target). A known method for sweeping a light beam across a bar code includes a stepper motor used to turn a mirror arrangement as shown in FIG. 2. A light source (laser or LED) is beamed onto the surface of the mirror. The mirror is rotated beta degrees by the stepper motor which causes the light beam to sweep through an angle of two beta degrees across a target (e.g. a bar code).
Another method for sweeping a light beam across a target includes the use of a miniature motor attached to a polygon mirror whose rotation is controlled by the motor, as shown in FIG. 3. Each surface or face of the "rotating" polygon is highly polished and functions as a mirror causing a light beam incident on the surface of the polygon to sweep across the target.
A significant problem with the prior art design is the power consumed by these systems. For example, the stepper motor of FIG. 2 requires 50 milliamperes at a voltage of 12 volts, which is equal to 600 milliwatts and the motor to drive the mirror of FIG. 3 requires 24 milliamps at a voltage of 12 volts, which is equal to 288 milliwatts. Thus, an object of the invention is to overcome the power consumption problem present in the prior art. This is particularly so in applications which are intended to be battery operated,
It is also an object of the invention to have a scanning system for use in applications, such as bar code readers (or scanners), where it is required that the system be portable, be of light weight, and be highly compact and have very few moving parts.